1. Field of the Invention
The invention relates to a flow control system for controlling the flow of process gas to a process chamber and a method of operating and, in particular, a flow control system for and method of controlling a multizone gas distribution system.
2. Description of Related Art
The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a processing chamber necessary to remove material from and deposit material on a substrate. In general, plasma is formed within the processing chamber under vacuum conditions by heating electrons in the presence of an electric field to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber (e.g., etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate).
In plasma processing systems, the uniformity of process results across the substrate are affected by spatial variations in plasma density within the process space above the substrate, typically expressed as a spatial distribution of electron density ne(r,θ), spatial variations in process chemistry (i.e., spatial distribution of chemical species), and spatial variations of the substrate temperature. Often times, the residence time τ(r,θ) of chemical species in the process space may be correlated with the amount of plasma dissociation occurring due to interactions between chemical constituents and energetic electrons and, hence, the residence time may be correlated with process chemistry; i.e., the greater the residence time, the greater the amount of dissociation of chemical constituents and the lesser the residence time, the lesser the dissociation of chemical constituents.
Common to many of these systems, the process gas is introduced to the process chamber through a showerhead gas distribution system having a plurality of gas passages formed there through. Therefore, in an effort to affect spatial variations in the process space above a substrate, multizone gas distribution systems have been contemplated. However, there remains a need to control the flow properties of the multizone gas distribution system.
Furthermore, the processes described above are sensitive to the conditions achieved within the plasma processing system and, in order to meet expected yields, precise control of these conditions is now required. For example, changes in these conditions due to either abrupt changes (or faults), or gradual changes require constant monitoring. Therefore, it is of increasing importance to detect fault conditions, determine whether the fault is real or erroneous, and determine if a service condition is present.